Cell cycle-dependent Cu uptake explained the heterogenous responses of Chlamydomonas to Cu exposure

Heterogeneous Single-Cell Distribution of Trace-Level Metal Mixtures in Tetrahymena thermophila Using Mass Cytometry

The uptake of heavy metals by unicellular organisms can lead to the bioaccumulation of these metals in higher organisms, detrimentally affecting organismal health and ultimately impacts the ecosystems. By studying the uptake and accumulation of heavy metals in unicellular organisms, we gain insights into potential risks associated with low-dose heavy metal exposure in aquatic environments. Thus, to investigate the accumulation characteristics of Mo, Ag, Cd, Sn, Sb, Hg, Tl, and Pb mixtures in single Tetrahymena thermophila cells, we developed a label-free approach for the simultaneous absolute quantification of multiple metals in a single cell using mass cytometry. Our results demonstrated the dynamic changes in metal concentrations in T. thermophila, and the competition between metals in uptake and excretory pathways resulted in heterogeneous accumulation and bioconcentration of these metals. Additionally, our findings revealed the limited capacity of T. thermophila to excrete Cd and Hg, suggesting a higher risk for T. thermophila cells when exposed to Cd and Hg over an extended period. Therefore, the current study provides valuable data for a more comprehensive understanding of the impact of low-dose heavy metals on aquatic ecosystems.

Intestinal Cu(II)/(I) Redox State Transformation Causes Cu(I) Overflow and Toxicity of the Gut and Liver in Zebrafish

Copper (Cu) has long been a concern for human health. While previous studies have explored the toxic effects of Cu, no study is available on the relationship between the Cu redox state transformation and biotoxicity in higher organisms. In this study, we explored the gut and liver toxicity caused by the overflow of Cu(I) at low doses of Cu exposure. Here, we first elucidated the digestive and metabolic systems as the main toxic target sites by a systematic epidemiological analysis. Then, ICP-MS analysis verified that the gut and liver were the top two Cu-high-accumulated organs in zebrafish exposed to 10 and 100 μg/L waterborne Cu for 72 h. In-situ Cu(I) and Cu(II) imaging techniques demonstrated that exogenous Cu(II) was converted to Cu(I) in the zebrafish gut. Furthermore, transcriptomic sequencing revealed that the high overflow of Cu(I) induced gut toxicity by cell cycle arrest in the G phase. However, the substantial accumulation of Cu(I) disrupted the metabolism of energy source nutrients and energy supply, leading to hepatic toxicity. This study provides new insights into the toxic mechanism based on Cu redox state and emphasizes the health risks associated with Cu exposure in the digestive and metabolic systems.

Robust Natural Light-Absorbable and -Degradable AIE Photosensitizers for Fluorescence Labeling and Efficient Photodynamic Eradication of Algal Pollutants

Current water pollution caused by the excessive proliferation of harmful algae urges green methods that can efficiently utilize natural light to treat algal pollution. Herein, a series of aggregation-induced emission (AIE) photosensitizers that can efficiently harness sunshine were synthesized for the environmentally friendly and biocompatible treatment of algal pollution. By tuning the number of thiophene units and the electron conjugation degree, the photosensitizers' absorptions were broadened to cover the whole visible light range. The positive charges guided photosensitizers to aggregate on algal cell surfaces, resulting in a turn-on fluorescence signal and robust reactive oxygen species generation under sunshine, thereby achieving fluorescence labeling and photodynamic eradication of algae. The eradication outcomes demonstrated that the AIE photosensitizers significantly outperformed the commercial algaecide ALG. At 20 ppm photosensitizers, 90.4% and 94.2% killing rates were achieved for C. reinhardtii and C. vulgaris, respectively, 2.8- and 3.6-fold higher than those from the same concentration of ALG. Excellent performances in inhibiting algae growth were also verified with efficiency superior to that of ALG. Importantly, the photosensitizers can self-degrade into biocompatible fragments under irradiation to avoid secondary pollution. The developed photosensitizers that possess sunshine convertibility and degradability provide an efficient tool for algal treatment, showing broad research and application prospects.

Dynamic Regulation of Intracellular Labile Cu(I)/Cu(II) Cycle in Microalgae Chlamydomonas reinhardtii: Disrupting the Balance by Cu Stress

The labile metal pool involved in intracellular trafficking and homeostasis is the portion susceptible to environmental stress. Herein, we visualized the different intracellular distributions of labile Cu(I) and Cu(II) pools in the alga Chlamydomonas reinhardtii. We first demonstrated that labile Cu(I) predominantly accumulated in the granules within the cytoplasmic matrix, whereas the labile Cu(II) pool primarily localized in the pyrenoid and chloroplast. The cell cycle played an integral role in balancing the labile Cu(I)/Cu(II) pools. Specifically, the labile Cu(II) pool primarily accumulated during the SM phase following cell division, while the labile Cu(I) pool dynamically changed during the G phase as cell size increased. Notably, the labile Cu(II) pool in algae at the SM stage exhibited heightened sensitivity to environmental Cu stress. Exogenous Cu stress disrupted the intracellular labile Cu(I)/Cu(II) cycle and balance, causing a shift toward the labile Cu(II) pool. Our proteomic analysis further identified a putative cupric reductase, potentially capable of reducing Cu(II) to Cu(I), and four putative multicopper oxidases, potentially capable of oxidizing Cu(I) to Cu(II), which may be involved in the conversion between the labile Cu(I) pool and labile Cu(II) pool. Our study elucidated a dynamic cycle of the intracellular labile Cu(I)/Cu(II) pools, which were accessible and responsive to environmental changes.

A surge of copper accumulation in cell division revealed its cyclical kinetics in synchronized green alga Chlamydomonas reinhardtii

Trace transition metal uptake is tightly associated with cellular biological processes. Herein, we demonstrated that copper (Cu) bioaccumulation and uptake were controlled by the cell cycle. A cyclical kinetics of Cu bioaccumulation and surge in S/M phase were observed in the synchronized green algae Chlamydomonas reinhardtii. The labile Cu(I) content also increased in the S/M phase, although the increase was moderate. Based on the comparative analysis of bioaccumulation and transcriptome data, we found the CRR1-mediated Cu uptake pathway, and CTR1 and CTR2 transporters were regulated by the intracellular Cu quota and suppressed during cell division with high Cu content. In contrast, we hypothesized a novel intracellular Cu-quota-independent Cu(I) uptake pathway in which the transporter COPT1 might be responsible for the Cu influx during cell division. Besides, a plunge of ATX1 expression level was also observed during cell division, which indicated an inhibition of the secretory pathway of Cu with the participation of ATX1 in terms of transcriptome level, probably resulting in reduced Cu efflux. Additionally, both fluorometric probe staining and transcriptomic data demonstrated that mitochondria were the dominant destination for the extra Cu content in S/M phase. Finally, some cytotoxic responses were also observed in S/M phase. Pathways related to reactive oxygen species and glutamine metabolic process were enriched in GO term and KEGG enrichment analysis, and glutathione content and cell membrane permeability determined by fluorometric probes also increased during cell division. This study showed a sharp increase of Cu uptake in cell division and revealed the genetic regulation mechanisms for the cell cycle control of Cu uptake.